The present invention relates an aromatic polyimide laminate comprising an aromatic polyimide composite film, a metal film, and a release film.
Aromatic polyimide films show good high temperature resistance, good chemical properties, high electrical insulating property, and high mechanical strength, and therefore are widely employed in various technical fields. For instance, an aromatic polyimide film is favorably employed in the form of a continuous aromatic polyimide film/metal film composite sheet for manufacturing a flexible printed circuit board (FPC), a carrier tape for tape-automated-bonding (TAB), and a tape of lead-on-chip (LOC) structure.
The aromatic polyimide film/metal film composite sheet can be produced by bonding a polyimide film to a metal film using a conventional adhesive such as an epoxy resin. However, due to low heat-resistance of the conventional adhesive, the produced composite sheet cannot show satisfactory heat-resistance.
For obviating the above-mentioned problem, a variety of bonding methods have been proposed. For instance, an aromatic polyimide film/metal film composite sheet is manufactured by forming a copper metal film on an aromatic polyimide film by electro-plating. Otherwise, an aromatic polyamide solution (i.e., a solution of a precursor of the aromatic polyimide resin) is coated on a copper film, dried, and heated for producing a polyimide layer on the copper film.
An aromatic polyimide film/metal film composite sheet can be produced using a thermoplastic polyimide resin.
U.S. Pat. No. 4,543,295 describes a polyimide laminate which is produced by applying a pressure onto a composite sheet composed of an aromatic polyimide film, a polyimide adhesive, and a metal film in vacuo.
Japanese Patent Provisional Publications No. 4-33847 and No. 4-33848 disclose an aromatic polyimide film/metal film composite sheet manufactured by means of a roll press, which may produce a continuous composite sheet.
According to studies of the present inventors, it is not easy to employ the roll press for producing a continuous composite sheet having a large width. Moreover, wrinkles, creases or rumples are sometimes observed on the surface of the polyimide film of the produced continuous composite sheet.
It is an object of the invention to provide an aromatic polyimide laminate in which a metal film is bonded to an aromatic polyimide film at a high bonding strength with good appearance and a release film is attached to another surface of the aromatic polyimide film at a releasable bonding strength.
It is another object of the invention to provide a continuous aromatic polyimide laminate having a large width (such as 400 mm or more), namely in the form of a continuous web, in which a metal film is bonded to an aromatic polyimide film at a high bonding strength with good appearance and a release film is attached to another surface of the aromatic polyimide film at a releasable bonding strength.
The present invention resides in an aromatic polyimide laminate comprising an aromatic polyimide composite film, a metal film, and a release film, the aromatic polyimide composite film being composed of an aromatic polyimide substrate film and two thermoplastic aromatic polyimide layers, each of which is fixed to each surface of the substrate film, the substrate film having no glass transition temperature of lower than 350xc2x0 C., the thermoplastic aromatic polyimide layer having a glass transition temperature of 190 to 280xc2x0 C., in which the metal film is fixed, with no intervening adhesive layer, to one thermoplastic aromatic polyimide layer at a 90xc2x0 peel strength of 0.8 kg/cm or more and the release film is fixed, with no intervening adhesive layer, to another thermoplastic aromatic polyimide layer at a 90xc2x0 peel strength of 0.001 to 0.5 kg/cm, under such condition that the latter peel strength is one half or less of the former peel strength.
The above-mentioned aromatic polyimide laminate can be produced by a method comprising simultaneously pressing the metal film onto one side of the aromatic polyimide composite film and the release film onto another side of the aromatic polyimide composite film by means of a double belt press.
A representative double belt press is described in U.S. Pat. No. 4,599,128, and is commercially available from Held Corporation (Germany).
The present invention is very favorably employed for producing an aromatic polyimide laminate in the form of a continuous web having a width of 400 mm or more, particularly a width of 500 mm or more.